Iron alloys are widely used in industries. Stainless steels, alloy steels and carbon steels are important engineering materials based on iron. To make complex or large iron alloy structures, iron alloy parts or components can be joined by welding or brazin. Brazing is a joining technology in which structures with high joint strength and corrosion resistance can be made. Brazing technology is well suited for bonding of complicated parts, for example, in the production of heat exchangers and honeycomb panels. Properties of joints made by brazing are strongly dependent on filler alloy properties, such as melting temperature and composition. Advantageously, filler alloys have melting temperatures high enough to enable rapid surface-bonding reactions with base materials and yet low enough to minimize phase transformations and microstructure-coarsening of base materials, which can save brazing time and energy. When corrosion resistance of the bonded structure is an additional requirement it is beneficial that the filler material be of similar composition to the base material or include elements that impart self-passivations to the base material and the joint between base and filler material.
Prior art filler alloys for steels are mainly nickel or copper based alloys. Their melting temperatures are typically higher than 1000° C., from which it follows that brazing with the filler alloys requires a temperature around 1100° C. At this temperature most steels recrystallize easily and develop a coarse grain structure. Additionally, copper and nickel are nobler than iron and can produce unfavorable electrochemical potential in a corrosive environment that attacks the iron/steel near the Cu or Ni-containing braze joint. These prior art alloys have other disadvantages, namely the raw material cost of nickel and copper is relatively high, and their filler-metal compositions are greatly different from the iron-base material. Therefore, development of new iron-based filler alloys with melting temperature less than 1000° C. can overcome some of the disadvantages of the prior art filler metals for the brazing of steels.